Process of making extended pigment with improved tinting strength



Patented Oct. 20, 1942 PROCESS OF MAKING EXTENDED PIGMENT WITH IMPROVED TINTING STRENGTH Kenneth S. ltlowlds Baltimore, Md., assignor to The Glidden Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Application August 2, 1940,

Serial No. 350,057

2 Claims. (Cl. 106-234) The present invention relates to the produc tion of pigments and has particular reference to the manufacture of extended pigments employing barium sulfate as an extender.

Among the objects of this invention is the pro-' vision of a process for making composite pigment of high, improved tinting strength.

More specifically, it is an object of this invention to provide a process for producing'lithopone and other extended pigments of high, improved tinting strength in a highly efiicient and simple manner.

Other, further and more specific objects of this invention will become readily apparent to persons skilled in the art from a consideration of the following description:

The use of barium sulfate as an extender for pigments is well known. In lithopone, zinc sulfide is extended with barium sulfate. Barium sulfate as an extender for titanium. dioxide is also well known.

According to the present invention, there is provided a process for producing barium sulfate which, when used as an extender for such pigments as zinc sulfide, zinc oxide, cadmium sulfide, cadmium reds, whilte lead and titanium oxide, results inan extended pigment of improved tinting strength.

I have foundthat the desired objects of the present invention maybe obtained by precipitating the barium sulfate from a barium sulfide solution by means of a sulfate of a metal of the alkali metal group, such as potassium sulfate,

sodium sulfate and lithium sulfate.

Also, in the manufacture of litliopone, if the precipitation is carried out in the presence of an excess of potassium sulfate, preferably in such a manner that the barium sulfate is precipitated by the potassium sulfate and the zinc sulfide by the liberated potassium sulfide, a lithopone of improved tinting strength is produced.

The reactions involved may be represented as By conducting the strike under conditions which minimize the direct reaction of the barium and zinc liquors and which facilitate the precipitation of the barium sulfate with K280; and the precipitation of the zinc sulfide with K2S the desired results are obtained. 1

- One manner in which these conditions may be to the strike tank at as widely separated points as possible and to employ a mild agitation sufiicient to transfer the K28 liberated by Equation 1 to the point of introduction of the zinc liquor and to transfer the K2804 liberated by Equation 2 to the point of introduction of the barium liquor,

without sufiicient agitation, however, to bring about substantial precipitation by direct reaction of the barium sulfide and zinc sulfate. Other modes of effecting precipitation of the BaSO4 and ZnS by the K2804 and K2S present, while minimizingdirect reaction between the barium and zinc liquors, may also be employed.-

The K2S04 may be added to either the barium liquor, the zinc liquor, or to water added with the zinc and barium liquors in the strike tank. The

progress of the reactions taking place when the K2804 is added to the barium liquor is as follows: The strike. is preferably started in a tank containing some water and the two solutions'introduced at widely separated points. Upon addition of the K2S04 to the barium liquor some BaSO is precipitated with the formation of KzS, so that the barium liquor in the strike tank contains BaS, K28 and BaS04. Mild agitation is employed and, when the K28 is transferred to the point of introduction of the zinc liquor, zinc sulfide is precipitated and K2804. formed. Of course, some co-precipitation of barium sulfate and zinc sulfide will take place when the strike is first started, but this can be minimized by the presence of some K2804 and/or K2S in'the water used to start the strike. However, as the strike proceeds an excess of K2S04 is formed and the direct reaction between barium and zinc liquors substantially or completely prevented. The E804 liberated by the reaction at the point of introduction of the zinc liquor is transferred back to the point at which the barium liquor is introduced, resulting in the precipitation of BaSOr and the reformation of ES.

Soon after the strike is started the concentration'of K2804 and X25 in the solution is such that the separate precipitation of the BaSOw. and ZnS can be effected without any direct reaction between the barium and zinc liquors.

Examples of carrying out this invention are as follows:

Example I To a barium sulfide liquor containing 225 grams BaS per liter is added twice the volume of K2804 solution containing 115 grams of K2804 per liter. The precipitate of B21304 is filtered off. washed and then mixed. with calcined titanium obtained is to add the barium and zinc liquors 5 oxide in the proportions of 30' parts H02 and parts B21804. The mixture is then heated to approximately 700 C.

The extended pigment, thus produced, has a tinting strength of 180, as compared to a tinting strength'of 145-150 for commercial Ti02Ba8O4 pigment (having the same 30. to '70 ratio).

4 Example II Example III To a barium sulfide liquor containing 225 grams BaS per liter is added twicethe volume vof K2804 solution containing 115 grams K2804 per liter. vThe precipitate of 39,804 is filtered off and then washed thoroughly. It is then mixed with calcined T102 in the proportions of 30 parts Ti02 J and '70 parts Ba8O4 and the mixture dried without calcining.

' Example IV To a barium sulfide liquor containing 225 grams BaS per liter is'added twice the volume of Na2804solution containing 115 grams of Na2804 per liter. The precipitate of M804 is filtered off, washed and then mixed with calcined titanium oxide in the proportions of 30 parts Ti02 and 70 parts Ber-804. The mixture is then heated to approximately 700 C.

v Example V To a. barium sulfide liquor containing 225 grams BaS per liter is added twice the volume of K2804 solution containing 115 grams K2804 perliter. Theprecipitate of Ba804 is filtered oil and then washed thoroughly. It is then calcined at approximately 700 0., and then mixed with calcined Zn in the proportions of 50 parts ZnO and. 50 parts Ba8O4.

Example VI To a barium sulfide liquor containing 225 7 gramsBaS per liter is added twice the volume of K2804 solution containing 115'grams K2804 per liter. The precipitate of Ba804 is filtered ofi and then washed thoroughly. It is then calcined at approximately 700 C. and then mixed with calcined ZnS in the proportions of parts ZnS and 50 parts Ba804.

Example VII To a barium sulfide liquor containing 225 grams BaS per liter is added twicethe volume of K2804 solution containing 115 grams K2804 per liter. The precipitate of Ba804 is filtered ofi and then washed thoroughly. It is then calcined at approximately 700 0., and then mixed with calcined CdS in the proportions of 30 parts CdS and 70 parts Ba804.

Example VIII To a barium sulfide liquor containing 225 grams BaS per liter is added twice the volume of K2804 solution containing 115 grams K2804 per liter. The precipitate of 311804 is filtered off and then washed'thoroughly. It is then calcined at approximately 700 C.,.and then mixed with calcined CdS and calcined ZnS in the proportions of 25 parts CdS, 5 parts ZnS and 70 parts Example IX To a barium sulfide liquor containing 225- grams BaS per liter is added twice the volume of K2804 solution containing 115 grams K2804 per liter. The precipitate of Ba804 is filtered oil and then washed thoroughly. It is then calcined at approximately 700 0., and then mixed with calcined Cd8.8ex in the proportions of 25 parts Cd8.8ex and parts Ba8O4.

In the foregoing examples, the extender Ba804 and the pigment may be mixed either dry or in a Example X To a barium sulfide liquor containing 225 grams BaS per liter is added twice the volume of K2804 solution containing grams K2804 per liter.

The precipitate of Ba804 is filtered oil and then washed thoroughly. It is then calcined at approximately 700 C. It is then mixed with white lead in the proportions of 75 parts white lead and 25 parts E2180; and the mixture dried without 1 calcining. v

If desired, the Ba804 formed in Example X can be used in uncalcined condition for mixing with the white lead.

Example XI To a liquor containing 225 grams BaS per liter are added 20 grams of K2804 per liter. The resulting liquor containing Ba8, K28 and some Ba804 is run into a strike tank, preferably at the top on one side, and zinc sulfate liquor containing 175 grams Zn804 per liter is run in preferably at the bottom onthe other side of the strike tank, the relative rates of introduction-of these liquors into the strike tank being regulated to produce a normal lithopone. Water is added to maintain the strike at approximately 9 Baum, the strike being made at about 75 C. Mild agitation is employed so that as the strike proceeds the K2804 and K28 are transferred to the points at which the respective liquors are added, but the agitation is insufficient to transfer zinc or barium liquors to cause direct substantial co-precipitation of the barium and zinc liquors. After the strike is complete, the lithopone is filtered, washed to remove soluble salts, ground and calcined in a manner conventional in the art. The calcined lithopone has a tinting strength of -150, as compared to a-tinting strength of 100-103 for normal lithopone prepared by the prior art method of direct co-precipitation of the barium and zinc liquors. Prior .to calcinationthe tinting strength of the lithopone is somewhat lower than that of the prior art uncalcined lithopone.

It is believed that the Ba804 prepared according to the present invention results in a-better extending of the pigment. However, the invention is not restricted by any theory advanced.

In the manufacture of lithopone according to the method described the amount of the improvement in tinting stren'gth is dependent somewhat upon the degreeeto which direct co-precipitation of the bariun gdnd zinc liquors is retarded or prevented. For some purposes it is not however, necessary to absolutely prevent direct coprecipitation as considerably improved results can be obtained even when there is an appreciable amount of direct reaction between the two liquors. However, best results are obtained if direct reaction is substantially retarded or prevented. Lithopone having a tinting strength of at least -30% in excess of the tinting strength of the corresponding extended pigment produced by direct reaction between barium sulfide and zinc sulfate, that is, with a tinting strength of 125-150 on the basis above referred to is readily obtainable, and tints as high as 150 to 155 or higher have been obtained. For best results it is preferred to add the liquors to the strike tank at as widely separated points as possible, and to employ only mild agitation. Under such conditions with an excess of K2804 present, there will be substantially no direct co-precipitation and the optimum results of the present invention will be obtained.

Example XII To a liquor containing 225 grams BaS per liter are added 15 grams of 1.12804 per liter. The resulting liquor containing H28, H28 and some 138.804 is run into a strike tank, preferably at the top on one side, and zinc sulfate liquor containing 175 grams Zn804 per liter is run in preferably at the bottom on the other side of the strike tank, the relative rates of introduction of these liquors into the strike tank being regulated to produce a normal lithopone. Water is added to maintain the strike at approximately 9 Baum, the strike being made at about 75 C. Mild agitation is employed so that as the strike proceeds the ,Li2804 and L128 are transferred to the points at which the respective liquors are added, but the agitation is insufllcient to transfer zinc or barium liquors to cause direct substantial co-precipitation of the barium and zinc liquors. After the strike is complete, the lithopone is filtered, washed to remove soluble salts, ground and calcined in a manner conventional in the art.

Example XIII Barium sulfide liquor containing 225 grams BaS per liter is struck simultaneously with the Cd804 liquor containing 220 grams CdSO4 perliter and a solution of K2804 is also simultaneously added in a sufficient quantity and at suflicient rate to maintain 10 grams per liter K2804 in the resulting strike liquor from the beginning to the end of the run, during which time the volume of strike liquor is increased. The BaS liquor and the Cd804 liquor are fed into the strike tank at relative rates to produce a normal cadmium lithopone. The Cd804 solution is preferably fed into the bottom of the strike tank on one side and the barium liquor preferably at the top on the opposite side. The &804 liquor is preferably fed in at the top. Water is added to maintain the strike at approximately 9 Baum, the strike being made at 75 C. Mild agitation is employed so that as the strike proceeds the K2804 and K28 are transferred to the points at which the respective liquors are added, but the agitation is insuflicient to transfer the cadmium or barium liquors to cause direct substantial coprecipitation of the barium and cadmium liquors. After the strike is complete, the lithopone is filtered, washed to remove soluble salts, ground Example XIV To a liquor containing 225 grams BaS per liter are added 20 grams of K2804 per liter. The

resulting liquor containing BaS, K28 and some Mild agitation is employed so that as the strikeproceeds the K2804 and K28 are transferred'to the points at which the respective liquors are added, but the agitation is insuflicient to transfer the cadmium-zinc or barium liquors to cause direct substantial co-precipitation of the barium and cadmium-zinc liquors. After the strike is complete, the lithopone is filtered, washed to remove soluble salts, ground and calcined in a manner conventional in the art.

Example XV To a liquor containing 225 grams BaS per liter and .35 grams selenium per liter are added 20 grams of K2804 per liter. The resulting liquor containing Ba8.8ex, K2s.sex and some BaSOr is run into a strike tank, preferably at the top on one side, and Cd804 liquor containing 220 grams C1180; per liter is run in preferably at the bottom on the other side of the strike tank, the relative rates of introduction of these liquors into the strike tank being regulated to produce the desired red tint and cadmium,selenium content lithopone. Water is added to maintain the strike at approx imately 9 Baum, the strike being made at about C. Mild agitation is employed so that as the strike proceeds the K280; and KzS.8ex are trans ferred to the points at which the respective liquors are added, but the agitation is insufiicient to transfer the cadmium or barium liquors to cause direct substantial co-precipitation of the barium and cadmium liquors. After the strike is complete, the lithopone is filtered, washed to remove soluble salts, ground and calcined in a manner conventional in the art.

In the foregoing examples, the concentration of the salts employed in the reactions are typical for operating conditions suitable for the respective processes. However, it is to be understood that solutions having different concentrations of these salts may also be employed within the scope of this invention. For example, the concentration of K2804 or other alkali metal sulfate employed in the strike tank may vary from 24o grams per liter. The K28 may also be varied from 2-40 grams per liter.

This invention may be employed for the production of normal typesof lithopone wherein the ZnS, CdS and/or Cd8.8e,= content is substantially equal to the stoichiometric equivalent of the B8804 thereof, as well as of lithopones wherein the Zn8, CdS and/or CdS.8ex content is either lower or higher than the stoichiometric equivalent of the BaSOr thereof. The improvement in tinting strength and covering power of the lithopones produced by this invention varies with the differences in the chemical compositions of these pigments but, irrespective of the differences in composition of the lithopones, I have found that the lithopones prepared according to the present invention show decided increase and improvement in tinting strength over lithopones of corresponding chemical composition prepared by the methods heretofore employed.

While certain theories and explanations have been advanced they are intended by way of explanation and not of restriction since various changes and modifications may be made by those skilled in the art without departing from the spirit of the invention. Other modes of minimizing the direct co-precipitation of the zinc and barium liquors and of facilitating the precipitatherein without departing from the spirit and scope of this invention, it is desired that only tion of BaS liquor with K2804 and the ZnSOr liquor with the K28 may be employed.

In the foregoing specification and the following claims wherever liquors or solutions of BaS and KzS are mentioned, it is to be understood that these references apply to the products resulting to apply to the products resulting from the solution of these sulfo-selenides in water.

The present invention is' not limited to the specific details set forth in the foregoing examples which should be construed as illustrative and not by way of limitation, and in view of the numerous modifications which may be eifected such limitations be imposed as are indicated in the appended claims.

I claim as my invention:

1. The process of producing an extended pig- 'nent of improved tinting strength comprising forming a precipitate of BaSO4 and ZnS, the precipitation of the B3504 and ZnS being eilected respectively by the simultaneous reaction or BaS with the sulfate of an alkali metal and of ZnSO; with the sulfide of an alkali metal, said sulfate of alkali metal and sulfide of alkali metal existing in the same aqueous bath and being continuously regenerated simultaneously in the process and said precipitation being effected without substantial direct reaction between the barium and zinc liquors by introducing the BaS and ZnSOs at places in the aqueous bath remote from each other.

2. The process of producing an extended pigment of improved tinting strength comprising forming a precipitate of B21804 and ZnS, the precipitation of the BaSO; and ZnS being effected respectively by the simultaneous reaction of BaS with K2804 and of ZnS04 with KzS, said &SO4 and ms existing in the same aqueous bath and continuously regenerated simultaneously in the process and said precipitation being eflected without substantial direct reaction between the barium and zinc liquors by introducing the BaS and ZnSOr at places in the aqueous bath remote from each other.

KENNETH S. MOWLDS. 

